A pod of <a href="https://www.nationalgeographic.com/animals/mammals/o/orca/">orcas</a> hunts off the Norwegian coast. Orcas are specialist predators: They have finely-tuned strategies for hunting specific prey, like herring, which means they don't cope well with environmental change.

<a href="https://www.nationalgeographic.com/animals/birds/s/southern-rockhopper-penguin/">Southern rockhopper penguins</a> swim toward shore in the Falkland Islands. They use their flipper-like wings to dive fast and deep in search of prey like fish and krill.

Rockhopper penguins climb a steep cliff in the Falklands. Overfishing, pollution, and other perils have dramatically reduced the population of these gregarious birds.

A large colony of Cape <a href="https://www.nationalgeographic.com/animals/mammals/group/fur-seals/">fur seals</a> covers a beach near Cape Fria, Namibia. The seals are <a href="https://news.nationalgeographic.com/2016/09/wildlife-watch-cape-fur-seal-trade-Namibia/">hunted en masse</a> in Namibia for their oil and fur.

A great white shark catches a decoy seal, set out by researchers. The predators are often hunted for their fins and meat, and they're also caught accidentally, as bycatch in fishing nets.

Orcas work together to &quot;<a href="https://www.nationalgeographic.com/magazine/2015/07/orcas-feeding-cooperative-hunting-killer-whales/">carousel hunt</a>.&quot; Here, an orca drives herring toward the surface. Then members of the pod will bunch the herring together, giving others a chance to feed.

Researchers attempt to satellite tag <a href="https://www.nationalgeographic.com/animals/mammals/b/blue-whale/">blue whales</a> off the coast of California. Blue whales, the largest animals on Earth, were hunted to the brink of extinction in the early 20th century. They've made only a partial recovery.

Striped mullet fish swim in a lake in Florida's Fanning Springs State Park. Mullets are a common food source for many larger species. They can thrive in both salt water and fresh water and live all over the world.

Lionfish swim over a reef in the Red Sea. <a href="https://www.nationalgeographic.com/travel/destinations/north-america/united-states/florida/lionfish-hunt-explorer-flordia-keys/">Lionfish</a> are venemous and are considered invasive species in some parts of the world, particularly the Caribbean. They've thrived there, taking the place of other species, like the grouper, that have become overfished.

<p>Opalescant inshore squids lay more than 50,000 eggs at a time and live for six to nine months. Their rapid reproduction rate means that they're potentially positioned to evolve quickly enough to cope with perils such as plastic waste and warming waters.</p>

<a href="https://www.nationalgeographic.com/animals/fish/group/anglerfish/">Anglerfish</a> live deep in the ocean, where there is no light. Females, like the one seen here, &quot;host&quot; males on their bodies. The <a href="https://news.nationalgeographic.com/2018/03/anglerfish-mating-rare-video-spd/">males latch on with their teeth</a> and are permanent parasites.

Moon <a href="https://www.nationalgeographic.com/magazine/2018/10/jellyfish-species-reproduction-feeding-ocean/">jellyfish</a> are pictured off the coast of Alaska. They don't have a respiratory system and breathe by diffusing oxygen through the translucent membranes covering their bodies.

<p>A <a href="https://www.nationalgeographic.com/animals/fish/g/great-white-shark/">great white shark</a> swims off Seal Island, in South Africa. Great whites are long-living apex predators and evolve very slowly, making them particularly susceptible to deteriorating ocean conditions due to climate change.</p>

Thousands of <a href="https://www.nationalgeographic.com/animals/reptiles/o/olive-ridley-sea-turtle/">olive ridley sea turtles</a> emerge from the sea once a month to lay eggs on Ostional Beach, in Costa Rica. Dogs, storks, and vultures frequently prey on hatchlings and eggs—<a href="https://news.nationalgeographic.com/2015/11/151130-olive-ridley-turtles-egg-poaching-Mexico/">as do humans</a>.

Tourists visit Ostional Beach as turtles emerge to lay eggs. It's legal for residents of the beach community to dig up eggs to sell. The beach's management says that profits stay in the community and that less than 1 percent of the eggs laid every year are collected.

Female olive ridley sea turtles all emerge at the same time every month, usually the week before the new moon, to lay eggs. They dig out a cone-shaped hole in the sand, about a foot and a half deep, and lay their eggs inside.